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Kinetics of Brominated Flame Retardant (BFR) Releases from Granules of Waste Plastics Bingbing Sun, Yuanan Hu, Hefa Cheng, and Shu Tao Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.6b04297 • Publication Date (Web): 28 Nov 2016 Downloaded from http://pubs.acs.org on November 29, 2016
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Environmental Science & Technology
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Kinetics of Brominated Flame Retardant (BFR) Releases from
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Granules of Waste Plastics
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Bingbing Sun1,2, Yuanan Hu3, Hefa Cheng4*, Shu Tao4
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1 State Key Laboratory of Organic Geochemistry
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Guangzhou Institute of Geochemistry, Chinese Academy of Sciences
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Guangzhou 510640, China
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2 University of Chinese Academy of Sciences Beijing 100049, China 3 MOE Laboratory of Groundwater Circulation and Evolution
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School of Water Resources and Environment
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China University of Geosciences (Beijing)
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Beijing 100083, China
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4 MOE Key Laboratory for Earth Surface Processes
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College of Urban and Environmental Sciences
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Peking University
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Beijing 100871, China
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Submitted to: Environmental Science & Technology
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* Corresponding author phone: (+86) 10 62761070; fax: (+86) 10 6276 7921; e-mail:
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[email protected] ACS Paragon Plus 1 Environment
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Abstract
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Plastic components of e-waste contain high levels of brominated flame retardants (BFRs),
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whose releases cause environmental and human health concerns. This study characterized the
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release kinetics of polybrominated diphenyl ethers (PBDEs) from millimeter-sized granules
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processed from the plastic exteriors of two scrap computer displays at environmentally relevant
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temperatures. The release rate of a substitute of PBDEs, 1,2-bis(2,4,6-tribromophenoxy)ethane
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(BTBPE), from the waste plastics, was reported for the first time.
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abundant PBDE congeners in both materials (87-89%), while BTBPE was also present at
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relatively high contents. The release kinetics of BFRs could be modeled as one dimensional
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diffusion, while the temperature dependence of diffusion coefficients was well described by the
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Arrhenius equation. The diffusion coefficients of BFRs (at 30 C) in the plastic matrices were
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estimated to be in the range of 10-27.16 to 10-19.96 m2·s-1, with apparent activation energies between
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88.4 and 154.2 kJ·mol-1. The half-lives of BFR releases (i.e., 50% depletion) from the plastic
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granules ranged from thousands to tens of billions of years at ambient temperatures.
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findings suggest that BFRs are released very slowly from the matrices of waste plastics through
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molecular diffusion, while their emissions can be significantly enhanced with wear-and-tear and
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pulverization.
Deca-BDE was the most
These
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1. Introduction
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Flame retardants are a diverse group of chemicals added during the manufacturing of a range of synthetic materials to inhibit the ignition and spread of flames.1
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Being effective and relatively
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inexpensive, brominated flame retardants (BFRs) have been widely used in plastics, textiles,
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building materials, and electrical appliances since the 1960s.2
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diphenyl ethers (PBDEs) had been used in high volumes, with deca-, octa-, and penta-BDEs being
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the most common congeners on the global market.
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in fire prevention and fire safety, concerns on their environmental and health effects are growing.
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As they are mechanically mixed into the materials without formation of chemical bonds, flame
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retardants can diffuse slowly out of the product matrices.
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the environment, and because of their high lipophilicity, they bioaccumulate in the food chain and
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human bodies, and pose health risk.3,4
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environment and human heath, various regulations, such as the Restriction of Hazardous
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Substances Directive (RoHS) and the Waste Electrical and Electronic Equipment Directive
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(WEEE), had been issued to regulate their use in consumer products in the European Union
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(EU).5,6 The use of two groups of PBDEs with high biological toxicity, penta-BDEs and
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octa-BDEs, were banned by the EU in 2004,7 while deca-BDE (BDE-209) was phased-out in
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electrical and electronic equipment in 2008.8
Among BFRs, polybrominated
Although flame retardants play a critical role
Once released, BFRs are persistent in
Due to concerns on the negative effects of BFRs on the
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With the restrictions placed on the use of PBDEs in consumer products, new BFRs have been
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developed
as
substitutes
for
the
banned
or
regulated
ones.
For
instance,
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1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE), first introduced in the mid-1970s, had been used
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as the replacement of octa-BDEs.9
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~16,710 tonnes in 20019), BTBPE has been detected in environmental and biotic matrices in many
As a result of its increasing use (~5,000 tonnes in 1997 and
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parts of the world.10,11 Although no direct health hazard has been identified for BTBPE so far, its
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thermal decomposition can produce precursors for the formation of polybrominated
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dibenzo-p-dioxins and dibenzofurans (PBDD/Fs),12,13 which have interim Toxicity Equivalency
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Factor (TEF) values comparable to those of the chlorinated congeners for human background
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exposure.14
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With the quick generation shift of consumer electronic products, waste electric and electronic
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products (e-waste) have become an increasingly important component in the solid waste stream. 15
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According to the estimation of the United Nations Environment Programme (UNEP), about 20-50
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million tonnes of e-waste is produced in the world annually, and this number is increasing
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rapidly.15
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processed and recycled in the developing countries, particularly China and India.
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estimated that about 70-80% of the e-waste generated in the US had been shipped to Asian
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countries for informal recycling.16
Large portion of the e-waste produced in some developed countries ends up being It was
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Recycling of e-waste in China has been carried out mostly in very simple and primitive ways,
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such as manual dismantling, open burning, and acid pickling.
E-waste recycling is profitable
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primarily through recovering the reusable or valuable electronic components and precious metals.
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As a result, the plastic components of electrical and electronic devices are often stripped, shredded,
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baked, or burnt to expose the metal components during various processes of recycling, and are
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sometimes burnt in open dumps to dispose of them.17,18
Releases of BFRs from the waste plastic
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were significantly enhanced due to the creation of fresh surface areas, elevated temperatures, and
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damages of the polymer structure, resulting in elevated concentrations of BFRs in local air.
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been reported that the concentrations of Σ22PBDEs in the atmosphere of Guiyu, a major e-waste
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dismantling area in southern China, were approximately 58-691 times higher than those in Hong
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Kong and Guangzhou.19 Similarly, the concentrations of Σ13PBDEs in the air of another major
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e-waste dismantling area, Taizhou in southeastern China, were about 7 times higher than that of
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background air.20
It has
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The release rates of BFRs from bulk plastic components of electronic products to air had been
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measured in controlled test chambers connected with narrow steel tubes for passive sampling of
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the air with polyurethane foam (PUF).21-23
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emissions and fate of BFRs by considering the environment media (e.g., air) and indoor goods as
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the sink and sources, respectively.24,25
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releasing behaviors of major BFRs from millimeter-sized granules processed from plastics of
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waste electronic products in the range of environmentally relevant temperatures. A diffusion
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model was derived to describe the release kinetics of the BFRs, while the apparent activation
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energies of the diffusion coefficients of BFRs were estimated from their temperature dependence
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using the Arrhenius equation. The results can help quantify and predict the long-term release
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potentials and risk of BFRs in pulverized plastic materials discarded from e-waste recycling in
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different climate zones. The findings can also be helpful for understanding and predicting the
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leaching behaviors of chemical additives present in microplastics.
Multimedia models were also used to estimate the
This work was conducted to systematically investigate the
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2. Experimental Section
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2.1. Model waste plastic materials
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The plastic rear cover of a cathode ray tube (CRT) monitor (manufactured in Malaysia in 1994),
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and that of a liquid crystal display (LCD) monitor (manufactured in China in 2005) were taken
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from scrap computers.
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styrene (ABS), were cut into pieces of approximately 1 cm by 1cm, chilled in liquid nitrogen, and
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then crushed into small granules in a metal grinder.
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were separated by stainless steel sieves (Supporting Information or SI Figure 1).
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the bulk plastic casings, such granules could better represent the shredded and crushed waste
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plastics that are dumped from e-waste recycling activities, while their significantly increased
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surface-area-to-volume ratios resulted in higher release fluxes of BFRs. The relatively controlled
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size ranges of plastic granules also facilitated normalization of the release fluxes to their surface
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areas.
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followed by triple-distilled water to remove the dusts and fine particulates attached to them.
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They were then air dried in a fume hood.
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determined by microwave-assisted extraction and gas chromatography-mass spectrometry (SI).
The plastic materials, both made primarily of acrylonitrile butadiene
Particles of 10-20, 30-40, and 50-100 meshes
All particles were soaked briefly in tap water, then rinsed carefully with flowing tap water,
The total contents of BFRs in the plastic granules were
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Compared to
2.2. BFR release experiment
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Kinetics of BFR releases from the plastic granules was evaluated in sealed vessels using PUF
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disks as the adsorbent.
Accurately weighted plastic granules of approximately 1000 mg were
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wrapped in copper wire mesh and inserted into 150 mL opaque wide mouth FEP bottles, followed
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by the pre-cleaned PUF disks (SI Figure 2). The bottles were then sealed and equilibrated in a
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dark constant temperature chambers at 10, 30, or 50 C.
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PUF disks were taken out of the FEP bottles and Soxhlet extracted using hexane/acetone (1:1, v/v)
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for 48 h at 60 C. The extracts were concentrated by rotary evaporation, blown down with
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nitrogen, and then solvent-exchanged into hexane to about 50, 300, or 1,000 μL, depending on the
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targeted analytes.
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Soxhlet extraction.
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adsorbed on the inside wall of FEP bottles, which were determined at the end of the BFR release
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experiments, were found to be much smaller (
